Polymer: make reproduce.sh check for tools it depends on

third_party/polymer/v1_0/reproduce.sh

Index: third_party/polymer/v1_0/reproduce.sh
diff --git a/third_party/polymer/v1_0/reproduce.sh b/third_party/polymer/v1_0/reproduce.sh
index ba895a4b48b1ecd6b7009c01d21d81a3c148d9e0..7c8833a5c130af0544edcfe57cf2564c7a599bf5 100755
--- a/third_party/polymer/v1_0/reproduce.sh
+++ b/third_party/polymer/v1_0/reproduce.sh
@@ -9,6 +9,20 @@
 # Chromium specific modifications. To launch the script you need 'bower' and
 # 'crisper' installed on your system.
 
+check_dep() {
+  eval "$1" >/dev/null 2>&1

[michaelpg, 2016/02/17 05:14:29]

why: eval "$1"
why not: which "$2"

[Dan Beam, 2016/02/17 17:22:31]

https://codereview.chromium.org/1702553002/diff/160001/third_party/polymer/v1...

as you found

+  if [ $? -ne 0 ]; then
+    echo >&2 "This script requires $2."
+    echo >&2 "Have you tried $3?"
+    exit 1
+  fi
+}
+
+check_dep "which npm" "npm" "visiting https://nodejs.org/en/"
+check_dep "which bower" "bower" "npm install -g bower"
+check_dep "which crisper" "crisper" "npm install -g crisper"
+check_dep "which rsync" "rsync" "apt-get install rsync"
+
 set -e
 
 cd "$(dirname "$0")"